1. Field of the Invention
The invention relates to a mixture-compressing, four-stroke internal-combustion engine with air-scavenging. More particularly, the invention relates to such an engine fitted with a first conduit by which, with scavenging valve and exhaust valve open, scavenging air is supplied to a cylinder at a pressure above atmospheric by means of an air charging system, and thereafter, with the exhaust valve closed, a mixture of air and fuel at a pressure above or under atmospheric is supplied to the cylinder through a second conduit containing a throttle valve, the engine output being determined by regulating the quantity of the air-fuel mixture supplied to the engine.
2. Description of the Related Art
An engine of the general type identified above is described in, for example, Netherlands Pat. No. 104,692. Since then the efforts of manufacturers and users of gas engines have been directed toward reducing NOx emissions, in response to the growing requirements that are being made to maintain the environment, and in particular the purity of the atmosphere. The measures that have been taken in this connection include making the air-fuel mixture leaner, while at the same time adapting the ignition devices and giving optimum shape to the combustion chamber and the inlet and outlet passageways to and from the combustion chamber. However, it has been established that those measures present problems that affect the life of the ignition devices, as a result of which a lean-mixture, high-compression engine of this design has not found wide acceptance on the market. A well known possibility of reducing the NOx content is reducing the temperature of the cylinder charge by cooling of the inlet air. The cooling system used in the engine in accordance with the invention permits the reduction of the NOx content in the exhaust gases with a less lean air-fuel mixture, i.e., at a smaller .lambda. value. In this way the problems with the ignition systems can greatly be avoided, opening the market for a new type of engine.